The present invention relates to a method for transmitting control information between a line-switching and a packet-switching communications network.
Originally, various types of communications networks were developed in order to transmit voice, data and video data. Owing to the various options for use of these communications networks, different services were developed. For example, Voicemail was developed for use in conventional line-switching communications networks, and electronic mail was developed for use in packet-switching communications networks, such as the Internet. As of today, voice, data and video services can be handled by both types of communications networks. Supplementary services (such a call transfer and call forwarding) can now also be used in packet-switching communications networks. At the present time, Standards are being defined and discussed, for example in the H.323-based series of ITU-T Recommendations (H.323, H.225, H.450: ITU-T Recommendations) for packet-switching communications networks. An H.323 architecture for supplementary services is described on pages 118–125 of an article titled “Supplementary Services in the H.323 IP Telephony Network” by Markku Korpi and Vineet Kumar published in the IEEE Communications Magazine in July 1999. The article describes one option for interaction of services between line-switching and packet-switching communications networks.
This article introduces a solution approach relating to the way in which user-channel-related signaling messages for controlling, requesting and (de)activating service features offered in the line-switching communications network can be mapped onto signaling packets used in the packet-switching network in accordance with a standardized transmission protocol. The signaling messages in the line-switching communications network are preferably DSS1 messages, as defined in the ITU Standards Q.931 and Q.932. The standardized H.225 signaling protocol is preferably used as the transmission protocol for the signaling packets in the packet-switching communications network, in particular in the Internet. Service features whose use requires user-channel-related signaling messages are, for example, call transfer, triple subscriber and large conference calls, hold, display charge information, closed user group and call number identification services.
There is currently no mapping capability for mapping signaling messages onto such signaling packets, such as those mentioned above, in the packet-switching communications network for signaling messages which are used in the line-switching communications network, are independent of the user channel or user connection and which, in particular, [lacuna] (de)activation or registration of service features for private branch exchanges (PBX) which are connected to the line-switching communications network. Signaling which is independent of the user channel or of the user connection is required, for example, for status checking and for activation and deactivation of service features such as call forwarding, call completion on busy subscriber or on no reply (automatic callback when busy or when there is no answer), outgoing call barring, and message waiting indication.
One feasible form of analog mapping of signaling messages which are independent of the user channel onto signaling packets in the packet-switching communications network based on the mapping of signaling messages which are dependent on the user channel onto signaling packets encounters, in particular, the difficulty that the DSS1 signaling messages used in the line-switching communications network are subject to a different type of transmission mechanism than that for the H.225 signaling packets used in the packet-switching communications network. The transmission of DSS1 signaling messages relates only to a local signaling section, that is to say between a communications terminal or private branch exchange and a switching center. In this case, the transmission of signaling messages is not terminated at the DSS1 protocol level, but is accomplished by means of subordinate protocol layers. In contrast to this, H.225 signaling packets are transmitted point-to-point, that is to say over a number of signaling sections, with the transmission of signaling packets being terminated only after receiving an acknowledgement at the H.225 protocol level. The concepts used in the line-switching communications network for transmitting signaling messages which are independent of the user connection have no corresponding concepts in the signaling protocols used in the packet switching communications network.